10. ELECTRIC ORGANS
433
the innervated face is relatively smooth and has only a few canaliculi
(Schwartz et al., 1971).
The electric organ discharge consists of what appear to be headpositive pulses superimposed on an almost level base line (Fig. 56).
However, the potential goes head-negative between pulses and as in
Sternop ygw, Eigenmannia, and sternarchids there is virtually no net
current flow during one complete organ cycle. (There is a small headpositive bump between the large pulses; this component is apparently
a result of nerve activity.) The absence of net current flow is a result
of the properties of the uninnervated face of the electrocytes. The
innervated face generates an ordinary spike when depolarized either
synaptically or by applied currents. The uninnervated face has a large
capacity and is of high resistance and inexcitable. Current flow through
it is virtually entirely capacitative. During a spike in the innervated
face the charge on the capacity of the uninnervated face is made more
positive; between spikes the charge on the capacity tends to return to
its initial value. The resulting external potential is diphasic and initially
positive outside the uninnervated face.
The sequence of potential changes and the cell equivalent circuit
are shown in Fig. 3E. The external medium behaves like an ohmic
resistance (at the frequencies of the electric organ discharge). The
external voltage is then proportional to the amplitude of transmembrane
current, and the integral over time of the external voltage gives a
measure of total current flow. Since the charge on the capacity of the
uninnervated face before and after a spike becomes the same during
a steady frequency of firing, no net current can flow through the
capacity and the time integrals of the positive and negative phases of
the external potentials must be equal. This they are observed to be
to within the 1 or 2% accuracy of the measurement.
The response of the single cells to depolarization applied by an
intracellular electrode is shown in Fig. 57 recorded both monopolarly
(Fig. 57A,B) and differentially (Fig. 57C,D). The monopolarly recorded potentials external to the two faces are diphasic and opposite
in sign (Fig. 57A,B) establishing the longitudinal orientation of the
cells. The potential outside the innervated face is initially negative
indicating that this face becomes active. The differentially recorded
potentials show a simple spike potential across the innervated face. The
potential across the uninnervated face is also a monophasic depolarization, but its peak is much lower and somewhat later. During the falling
phase, however, the potential across this face exceeds that across the
innervated face, which accounts for the head-negative phase in the
433
the innervated face is relatively smooth and has only a few canaliculi
(Schwartz et al., 1971).
The electric organ discharge consists of what appear to be headpositive pulses superimposed on an almost level base line (Fig. 56).
However, the potential goes head-negative between pulses and as in
Sternop ygw, Eigenmannia, and sternarchids there is virtually no net
current flow during one complete organ cycle. (There is a small headpositive bump between the large pulses; this component is apparently
a result of nerve activity.) The absence of net current flow is a result
of the properties of the uninnervated face of the electrocytes. The
innervated face generates an ordinary spike when depolarized either
synaptically or by applied currents. The uninnervated face has a large
capacity and is of high resistance and inexcitable. Current flow through
it is virtually entirely capacitative. During a spike in the innervated
face the charge on the capacity of the uninnervated face is made more
positive; between spikes the charge on the capacity tends to return to
its initial value. The resulting external potential is diphasic and initially
positive outside the uninnervated face.
The sequence of potential changes and the cell equivalent circuit
are shown in Fig. 3E. The external medium behaves like an ohmic
resistance (at the frequencies of the electric organ discharge). The
external voltage is then proportional to the amplitude of transmembrane
current, and the integral over time of the external voltage gives a
measure of total current flow. Since the charge on the capacity of the
uninnervated face before and after a spike becomes the same during
a steady frequency of firing, no net current can flow through the
capacity and the time integrals of the positive and negative phases of
the external potentials must be equal. This they are observed to be
to within the 1 or 2% accuracy of the measurement.
The response of the single cells to depolarization applied by an
intracellular electrode is shown in Fig. 57 recorded both monopolarly
(Fig. 57A,B) and differentially (Fig. 57C,D). The monopolarly recorded potentials external to the two faces are diphasic and opposite
in sign (Fig. 57A,B) establishing the longitudinal orientation of the
cells. The potential outside the innervated face is initially negative
indicating that this face becomes active. The differentially recorded
potentials show a simple spike potential across the innervated face. The
potential across the uninnervated face is also a monophasic depolarization, but its peak is much lower and somewhat later. During the falling
phase, however, the potential across this face exceeds that across the
innervated face, which accounts for the head-negative phase in the